262 SPECIFIC MICRO-ORGANISMS 



of the small colony surrounded by a very clear zone of hemolysis 

 which the streptococcus produces on this medium. In making 

 cultures from the blood in bacteremia, plain agar previously 

 melted and cooled to 45 C. is mixed with freshly drawn blood 

 of the patient and allowed to solidfy in a Petri dish. In other 

 cases naturally sterile defibrinated rabbit's blood may be used, 

 the technic of plating being analogous to that described for the 

 gonococcus. The streptococcus grows very slowly below 20 C. 

 and poorly in ordinary gelatin, which it does not liquefy. On 

 solid media, agar or serum-agar, at 37 C., small round elevated 

 colonies develop, 0.5 to i.o mm. in diameter, and they tend to 

 remain discreet. In broth only a slight cloud develops, but 

 considerable granular deposit made up of streptococci is found 

 at the bottom of the tube. Various carbohydrates are fermented 

 with the production of acid and without formation of gas, but 

 the behavior of streptococci toward these substances seems so 

 variable that the attempts to utilize the fermentative power as 

 a basis for classifying the streptococci has not led to wholly satis- 

 factory results. The differences in fermentative power seem to 

 depend more upon vigor of growth than upon essential qualita- 

 tive differences between the streptococci tested. 1 



The streptococcus is relatively very resistant to heat, at times 

 requiring one to two hours heating at 65 C. or one hour at 70 

 C. in order to insure sterility, according to V. Lingelsheim. 

 Most investigators have found 60 C. for twenty minutes suffi- 

 cient. Its poisons seem to be chiefly intracellular and set free 

 upon disintegration of the organisms. Soluble poisons have 

 nevertheless been found in some cultures. 



Laboratory animals are not very susceptible to inoculation 

 with streptococci. White mice and rabbits are most useful, 

 and they ordinarily succumb to intraperitoneal injection of 

 virulent strains. 



The enormous importance of the streptococcus as a cause 

 of sickness and death before the aseptic era is difficult to realize 



1 V. Lingelsheim in Kolle und Wassermann, Handbuch, 1912, Bd. IV, S. 462. 



